[The normal aspect of the suprapatellar bursa in echography of the knee]

Sonography is suitable to recognize fluids in the suprapatellar bursa, which can represent an indirect sign of intra-articular knee effusion. In order to obtain the physiologic parameters of suprapatellar bursa, 50 healthy volunteers, 38 sedentary and 12 sportsmen, were evaluated by means of US. The bursa was recognizable in 8/50 cases (16%) with quadriceps in prolapse (mean thickness: 1.8 mm, mean length: 20.5 mm), and in 23/50 cases (46%) with quadriceps in contraction (mean thickness: 2.6 mm, mean length: 22.6 mm). Suprapatellar bursal thickness ranged 1-4 mm, and its length ranged 12-44 mm. The suprapatellar bursa appeared as a well-defined hypoechoic band, cranial to patella, anterior to the distal femoral shaft, and posterior to quadriceps tendon. Quadriceps contraction increases both thickness and length of bursal swelling (1 and 2 mm, respectively, on the average). When sportsmen were compared with sedentary subjects, suprapatellar bursa diameters were observed not to change, but the bursal itself was evident in 3/12 (25%) and in 8/12 (66%) of cases, according to whether the quadriceps was in prolapse or in contraction. Bursal contents were homogeneously anechoic and bursal outline smooth and regular in all cases (23/23). Bursal morphology was symmetric, in 23/23 cases, in length, regularity of outline, and echogenicity of contents. Thickness alone resulted asymmetrical in 2/23 subjects (8%), even though variations were less than or equal to 2 mm. In conclusion, we can consider as pathologic features: thickness greater than 3-4 mm, asymmetry greater than 2 mm, irregular outline, and inhomogeneous contents. These parameters must be examined in pathologic subjects and further research is mandatory.